1. Field of the Invention
The present invention relates to a timer, and more particularly to a mechanical timer applicable to timer-operated household electrical appliances.
2. Related Art
Currently, commercially-available washing machines are mainly classified into two types, namely, microcomputer type and mechanical type. Taking a mechanical washing machine as an example, the time course is set by turning a knob, so as to start washing, rinsing, drying, and other functions at a particular time. For example, U.S. Pat. Nos. 6,441,326, 6,613,991, 6,797,897, 6,838,626 and 7,005,589 disclose a timer with a front housing and a rear housing. Contained within the front housing and rear housing are a timing motor and gear train assembly to drive a main cam. The main cam has geometry to be contacted by cam followers of switch arms. As the main cam rotates, the varying contours of program cam surfaces move the switch arms between neutral and offset positions. The movement of the switch arms relative to one another results in the activation and deactivation of electrical circuits which operate the cycles of the appliance to which the timer is associated. The timer includes a setting feedback (SF) system. By this SF system, cam followers are lifted off the program cam surfaces so that a “V”-shaped follower remains in contact with a custom feel profile on the side of the main cam proximal the front housing. This “V”-shaped follower acts as a tactile and/or audible feedback member, by engaging the textured surface of the custom feel profile to impart such tactile feel to the user during rotation of the main cam.
The timer has a shaft extending outside the housing for user to operate. Typically, the shaft has two operation positions along its axis, namely a setting position where the main cam surface and the cam follower of switch arms are lifted off; and a driving position where the main cam surface and the cam follower of switch arms contact. At the setting position, the main cam can be rotated by the user to an appropriate angular position to begin a timing cycle. At the driving position, the timing motor starts to drive the main cam. Usually, the timer shaft is pressed down to the setting position, and pulled up to the driving position.
There are some drawbacks in the aforesaid prior art timers. Firstly, since the switch arms are raised by an actuator beam mounted on the shaft, and the switch arms are all on one side of the cam, the force on the actuator is unbalanced that easily bends the beam. Secondly, the timer gear train requires a clutch mechanism which allows manual rotation of the main cam only in a forward direction in order to prevent any rotation of the cam in a reverse direction that will damage the timer components during manual operation of the main cam. Thirdly, the setting feedback (SF) system in the timer requires an additional “V”-shaped follower remaining in contact with a custom feel profile on the side of the main cam proximal the front housing; also, the steady contact between the “V”-shaped follower and the custom feel profile of the cam is not good in the cam driving state that it only causes friction, wearing of the components and resistance to the cam motion.